The production process of longitudinally welded pipes is relatively simple. The main production processes are high-frequency welded longitudinally welded pipes and submerged arc welded longitudinally welded pipes. The longitudinally welded pipes have high production efficiency, low cost, and rapid development. The strength of spiral welded pipe is generally higher than that of straight seam welded pipe. The main production process is submerged arc welding. Spiral steel pipe can produce welded pipes with different pipe diameters from the same width of blanks, and can also use narrower blanks to produce welded pipes with larger pipe diameters. But compared with the straight seam pipe of the same length, the weld length is increased by 30-100%, and the production speed is lower. Therefore, most of the smaller diameter welded pipes use straight seam welding, and the large diameter welded pipes mostly use spiral welding. T-welding technology is used in the production of larger-diameter straight seam steel pipes in the industry, which means that short sections of straight seam steel pipes are butt-joined to a length that meets the needs of the project. The probability of defects in T-welded straight seam steel pipes is greatly increased, and T-welding The welding residual stress at the seam is relatively large, and the weld metal is often in a three-dimensional stress state, which increases the possibility of cracks.

Welding process

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In terms of welding process, the welding method of spiral welded pipe is the same as that of straight seam steel pipe, but the straight seam welded pipe inevitably has a lot of T-shaped welds, so the probability of welding defects is greatly increased, and the welding residue at the T-shaped weld The stress is large, and the weld metal is often in a three-dimensional stress state, which increases the possibility of cracks.
Moreover, according to the submerged arc welding process regulations, each weld should have an arc ignition point and an arc extinction point, but each longitudinal welded pipe cannot meet this condition when welding the girth seam, so there may be an arc extinction point. More welding defects.

Strength characteristics

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When the pipe is subjected to internal pressure, two main stresses are usually generated on the pipe wall, namely radial stress δ and axial stress δ. The resultant stress δ at the weld, where α is the helix angle of the weld of the spiral welded pipe.
The helix angle of the spiral welded pipe weld is generally degrees, so the resultant stress at the spiral weld is the principal stress of the longitudinal welded pipe. Under the same working pressure, the spiral welded pipe with the same pipe diameter can be reduced in wall thickness than the straight seam welded pipe.
According to the above characteristics:
When the spiral welded pipe is blasted, because the normal stress and the resultant stress on the weld are relatively small, the blasting opening generally does not originate at the spiral weld, and its safety is higher than that of the straight seam welded pipe.
When there are defects parallel to the spiral weld near the spiral weld, because the spiral weld is less stressed, the risk of its expansion is not as great as that of the straight weld.
Since the radial stress is the maximum stress that exists on the steel pipe, the weld is subjected to the maximum load when it is in the direction of the vertical stress. That is, the load borne by the straight seam is the largest, the load borne by the circumferential weld is the smallest, and the spiral seam is between the two.

Static pressure blasting strength

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The yield pressures of spiral welded pipes and longitudinally welded pipes are basically consistent with the actual and theoretical values of burst pressure, and the deviations are close. However, both the yield pressure and the burst pressure of spiral welded pipes are lower than those of straight seam welded pipes. The blasting test also showed that the circumferential deformation rate of the spiral welded pipe blasting port was significantly greater than that of the straight seam welded pipe. This proves that the plastic deformation ability of spiral welded pipe is better than that of straight seam welded pipe, and the blast hole is generally limited to one pitch, which is caused by the strong restraint effect of spiral weld on the expansion of the crack.

Toughness and fatigue strength

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The trend of pipeline development is large diameter and high strength. As the diameter of the steel pipe increases and the grade of steel used increases, the tendency of the ductile fracture tip to expand steadily becomes greater. According to the test conducted by relevant research institutions in the United States, although spiral welded pipe and longitudinal welded pipe are at the same level, spiral welded pipe has higher impact toughness.
Due to changes in the transportation volume, the steel pipes are subjected to random alternating loads during actual operation. Understanding the low cycle fatigue strength of steel pipes is of great significance for judging the service life of pipelines.
According to the measurement results, the fatigue strength of spiral welded pipes is the same as seamless pipes and resistance welded pipes, and the test data is distributed in the same area as seamless pipes and resistance pipes, but higher than general submerged arc longitudinal welded pipes.

Steel pipes are essential components of various industries, including construction, oil and gas, and water transportation. When it comes to choosing the right type of steel pipe for your project, two options come to mind: straight seam steel pipe and spiral steel pipe. Both types have their own unique characteristics that make them suitable for specific applications. In this blog post, we'll compare the features of these two popular types of steel pipes to help you make an informed decision on which one will work best for your needs. Let's dive in!

Characteristics of straight seam steel pipe

Straight seam steel pipes are made by bending a single, long strip of steel into a cylindrical shape and then welding the edges together. This type of pipe is commonly used in industries such as construction and infrastructure due to its high strength and durability.

One of the key characteristics of straight seam steel pipes is their uniformity. The welded seams are consistent throughout the length of the pipe, which helps maintain structural integrity when under stress or pressure. Additionally, because there are no curves or bends in this type of pipe, it's easier to fabricate and install.

Another advantage of straight seam steel pipes is their affordability. They're relatively cheap compared to other types of pipes like seamless pipes, making them an attractive option for budget-conscious projects that require large quantities.

However, one disadvantage of straight seam steel pipes is that they have a tendency to crack easily at the welds if subjected to excessive strain or vibration. This can lead to leaks or even catastrophic failure if not detected early enough.

Straight seam steel pipes offer great value for money while providing excellent strength and durability but need careful attention during installation and usage due to susceptibility towards cracks at welds under stress.

Fracture of straight seam welded pipe

One of the major concerns with straight seam welded pipes is the risk of fracturing. Fractures can occur due to a variety of factors, including poor welding quality, stress from external forces, and material defects.

Poor welding quality can result in weak spots along the length of the pipe that are more likely to fracture under pressure. This is why it's important for manufacturers to use high-quality materials and ensure proper welding techniques are used during production.

Stress caused by external factors such as shifting ground or heavy machinery overhead can also contribute to fractures in straight seam welded pipes. Regular inspections and maintenance can help identify potential problem areas before they become serious issues.

Material defects such as cracks or impurities within the steel itself can also lead to fractures over time. It's important for manufacturers to conduct thorough testing on their raw materials before manufacturing begins.

While straight seam welded pipes do have a higher risk of fracturing compared to spiral-welded pipes, this risk can be mitigated through proper manufacturing practices and regular maintenance checks.

Spiral welded pipe strength

Spiral welded pipes are known for their high strength and durability. This is because of the welding process used in creating them. The continuous spiral weld creates a strong bond that can handle high pressure and stress.

The spiral weld also allows for greater flexibility, which makes it easier to navigate around obstacles or uneven terrain when laying pipelines. This type of pipe is commonly used in oil and gas pipelines, as well as water distribution systems.

Another factor contributing to the strength of spiral welded pipes is the quality of the steel used in their construction. High-quality materials ensure that the pipes can withstand external forces like corrosion, abrasion, and extreme temperatures.

The combination of high-quality materials and a continuous spiral weld make spiral welded pipes incredibly reliable and long-lasting. These qualities make them an excellent choice for applications where strength and durability are paramount concerns.

Impact of spiral welded steel pipe

In summary, both straight seam and spiral steel pipes have their unique characteristics and advantages. Straight seam steel pipes are great for high-pressure applications due to their strong resistance to stress. However, they may be more prone to fractures than spiral welded pipes.

Spiral welded steel pipe, on the other hand, is known for its strength and durability. It can withstand higher loads compared to straight seam welded pipes without fracturing or buckling easily. Additionally, it's easier to install since it comes in longer lengths which reduces welding time.

Choosing between these two types of pipes depends on various factors such as budget constraints, intended use of the piping system and installation requirements. Nonetheless, with this insightful comparison article , you can make an informed decision on what type of pipe will best suit your needs while ensuring optimal performance for a long time!

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